1. Field of the Invention
The invention relates to boat hull designs.
2. Description of the Related Art
It is well known in the industry that watercraft with a multi-hull design provide better seakeeping in moderate-to-high wave conditions than monohull vessels. Multi-hull ships can be designed to suffer only one-half to one-fifth of the heave, pitch, and roll motions of a monohull vessel of equal displacement in seas driven by wind speeds above 20 knots.
An additional benefit of multi-hull designs is they can travel at faster speeds than a monohull design. The wave penetrating features of a multi-hull design allow the watercraft to also maintain course and speed during sea conditions that would otherwise defeat a monohull's ability to maintain the same course and speed.
However, an inherent problem with multi-hull designs is, in the event of a roll-over, they do not return upright once capsized. A multi-hull vessel is equally stable capsized as it is upright. Monohull vessels do not have this problem.
Through innovative designs and concepts, various hull designs have been introduced. In an article titled "Variable Draft Broadens SWATH Horizons" in the April 1994 issue of Proceedings, improvements are made to the design known as Small Waterplane Area Twin-Hull (SWATH) ships. The SWATH design for this particular boat utilizes struts that are aligned on the centerline of the lower hull. The lower hull's rectangular cross sections enhance seakeeping at deeper drafts and give best propulsion at transit depths. The center bow provides a cushion against slamming and affords convenient overboard access for handling equipment. Rectangular hull forms supportive of the SWATH design are less expensive to fabricate and outfit than conventional hull designs.
The U.S. Navy test vessel, Sea Shadow, was built to test several aspects of maintaining stealthiness at sea, including low radar visibility, quietness to sonar sensors and minimizing wake. An article titled "The Secret Ship" in the October 1993 issue of Popular Science discussed the unclassified parameters of this vessel. Above the waterline, the Sea Shadow's resemblance is similar to that of the U.S. Air Force F-117A stealth fighter. From the waterline down, the exact details are classified, but the ship's underwater shape is essentially a SWATH design. A pair of submerged pontoons gives the Sea Shadow its buoyancy. Running beneath the water's choppy surface layer, these pontoons cause far less of the seasickness-inspiring vertical motion inherent in traditional monohull designs.
Another unique design is the trimaran hydrofoil designed and built by Greg Ketterman, as discussed in an article titled, "World's Fastest Sailboat," in the January 1991 issue of Popular Science. The hydrofoil is a two-mast, triple-hull design that utilizes sensors forward of the outer hulls that hug the water's undulating surface, constantly adjusting the pitch of the hulls and main foils to maintain stability and minimize drag. Foot pedals control the rudder. This design is primarily for sail boats that want to maximize speed through the waters.
Prior art multi-hull designs share the disadvantage that they are not self-righting in the event of a roll-over or if capsized, which is not the case with monohull designs. Also, multi-hull designs are not entirely constructed out of flat plate material, which is a factor in cost and complexity to build. Thus, a multi-hull design that is self-righting and easily constructed is not disclosed in the prior art.